500gb drive full

Hello,

I need some help badly. Less than a year ago I purchased a Dell Lap Top with Windows Vista and a 500GB hard drive. As of this morning I have only 38 gigs left! I checked all of my personal, system and program files and the only take up a very small portion of the hard drive and the biggest files are my photos (I am a photographer) but they only take up 78gigs of space. I have done a disk chk, disk cleanup, defrag, checked for viruses, etc. The computer came up clear for problems and viruses. I read on another forum of a person last year who had the same experience and said he figured out it was a Dell RA program. He disabled it and deleted the User and he got back 400+ gB of space. I have not clue how to do this.

My question is has anyone had a the same experience and how did they resolve it?